1. Field of the Invention
This invention relates to p-dinitrosobenzene on a support, to its production and to its use as a crosslinking aid.
2. Discussion of Related Art
p-Dinitrosobenzene (DNB) is a finely crystalline, dark green product which is only sparingly soluble in alcohol, xylene and water. It is supplied in the form of an approximately 25 to 50% suspension in aromatic hydrocarbons. It is used as a highly active crosslinking agent, for example in adhesives, and as a sulfur-free vulcanizing agent for synthetic and natural rubber mixtures.
Thus, DE 22 28 544 describes a binder for the production of composites by vulcanization of rubber mixtures onto metals or other stable substrates. In addition to chlorosulfonated polyethylene, chlorinated rubber, polyisocyanates and a phenolic resin, this binder also contains dinitrosobenzene in the form of a suspension in solvents.
In DE 34 00 852, DNB is described as a constituent of a moisture-curing one-component polyurethane lacquer for coating elastomers. The DNB may be used both in the form of a pure chemical substance and in the form of a 30 to 40% suspension in quantities of 0.5 to 4% by weight, based on the solventless lacquer resins.
In DE 34 00 340, DNB is described as a constituent of an adhesive for the electrostatic flocking of flexible substrates. The adhesive additionally consists of an isocyanate-terminated polyurethane prepolymer, a reaction product of polyfunctional epoxides with aromatic diisocyanates and solvents and/or dispersants. The DNB is present in quantities of 0.5 to 4% by weight, based on the solventless adhesive. It may be used both as a pure substance or as a solution or dispersion in nonsolvents. Although reference is made to a 30 to 40% by weight solution of dinitrosobenzene, for example in xylene, toluene or methyl isobutyl ketone, the dinitrosobenzene cannot be p-dinitrosobenzene because p-dinitrosobenzene only forms an approximately 2% solution in boiling xylene (see P. Ruggli and G. Bartusch in Helvetia Chimia Acta 27 (1944), page 1371 et seq.).
DE 30 35 181 describes a bonding agent based on an aqueous dispersion of an organic polymeric film former for bonding rubber to metallic or non-metallic substrates under vulcanization conditions, the dispersion containing adhesion-promoting additives, an aromatic polynitroso compound and optionally fillers. The aromatic polynitroso compound is inter alia dinitrosobenzene which is added as a 40% aqueous dispersion consisting of 5 parts of dinitrosobenzene, 1 part of carbon black and 9 parts of water in quantities of 10 to 100 parts by weight, based on the copolymer.
DE 12 72 301 describes the thermal stabilization of aromatic nitroso compounds by an addition of 20 to 200% by weight, based on the dinitroso compound, of a decomposable metal or ammonium salt or by addition of 0 to 234% by weight, based on the dinitroso compound, of a silicate-containing water adsorbent. MgSO.sub.4.7H.sub.2 O is preferably used as the salt. Calcium silicate, clay and other inert fillers and carriers are mentioned as adsorbents.
Although the known use of DNB in binders leads to permanent bonds, more particularly between synthetic or natural rubber and metals, and although the bonds thus obtained are also distinguished by high permanent strength and by high resistance to aggressive media, it is also attended by disadvantages. Unreacted DNB can give rise to continuing vulcanization in the event of subsequent heat treatment, resulting in unwanted embrittlement of the bond. DNB is also relatively expensive.